The forging rationale is likely very outdated now.
If I have a legal document where I need to be certain of its provenance after going out into the world, it is a digitally signed PDF.
If I print a paper check where the numbers need to be tamper-resistant against casual forging, I use a secure number font. I don't anticipate ever being in a position where my adversary in that use case is a determined, professional forger. I'd insist upon encrypted and/or insured electronic transactions, like through SWIFT or ACH, before I get to the point I'd be worried about professional forgers.
Sure, it's outdated now, but habits of accounting tend to die hard.
In Chinese, some characters representing numbers are so trivially forgible by adding a stroke or two (1 = 一, 2 = 二, 3 = 三, 10 = 十, 1000 = 千) that accountants came up with complicated substitutes that cannot be altered to mean any other number (1 = 壹, 2 = 贰, 3 = 叁, 10 = 拾, 1000 = 仟). The substitutes are still widely used in legal and financial documents.
If I have a legal document where I need to be certain of its provenance after going out into the world, it is a digitally signed PDF.
If I print a paper check where the numbers need to be tamper-resistant against casual forging, I use a secure number font. I don't anticipate ever being in a position where my adversary in that use case is a determined, professional forger. I'd insist upon encrypted and/or insured electronic transactions, like through SWIFT or ACH, before I get to the point I'd be worried about professional forgers.